An orphaned boy, Champion, is raised by his grandmother, Madame Souza. Her gift of a tricycle starts a craze for cycle-racing that becomes the cornerstone of their life together. After years of relentless training, Champion makes it to the Tour de France, the toughest cycling event in the world. Alas, Champion and a handful of other top competitors are mysteriously kidnapped by a pair of sinister crooks with hangdog expressions. Supported by her faithful sidekick, her fat and flatulent dog Bruno, Madame Souza sets off to rescue her beloved Champion. An epic adventure leads them across the Atlantic to a vast seaport metropolis named Belleville, headquarters of the notorious French mafia. Lost and confused in the threatening darkness of the great city, Madame Souza and Bruno encounter the Belleville Triplettes, who, in their youth, were a glamorous close-harmony act. Now, these three batty old women are now a bizarre jazz combo. Mme Souza joins the band. At their very first gig, she discovers Champion is being held captive by the mafia Godfather himself! All hell breaks loose, and the chase is on! Do Mme Souza, her dim dog, and the Triplettes have what it takes to outsmart the ruthless French mafia and release poor Champion from its clutches?